This ski technique in which the heel is not rigidly held on the ski, but is free to rise, requires the use of special ski boots. This type of ski boot has a flexible area in correspondence with the metatarsus.
Ski boots of this type are composed of a sole, a shell in plastic material which is integral with the sole, where the foot of the wearer is housed, and a leg piece hinged to the shell substantially at the ankle and designed to wrap the lower portion of the wearer's leg at the back and at the sides.
A tongue for the frontal closure of the ski boot is fixed to the upper frontal area of the ski boot, and lies inside the front lateral portions of the leg piece.
The ski boot is provided with closure members on the upper part of the shell and between said front lateral portions of the leg piece.
Said flexible area generally consists of a corrugated portion located on the shell in the area of the metatarsus o f the wearer; said corrugated portion has one or more grooves which extend transversely to the shell and which begin and end in proximity with the sole, on opposite sides of the shell itself.
The flexing of the corrugated portion causes lateral swelling of the shell in correspondence with said portion, and exposes it to rubbing on the other ski, and consequently to excessive wear with respect to the other parts of the ski boot.
The consequence of this precocious wear of the internal part of the corrugated portion on the inside of the ski boot is the precocious replacement of the entire ski boot, even though this may be in excellent condition in all other parts.